1. Field of the Invention
The present invention concerns an examination platform for a magnetic resonance apparatus with a movable patient bed, a movable local antenna device for acquisition of magnetic resonance signals, and a drive for moving the bed. The invention also concerns a magnetic resonance apparatus with such an examination platform as well as a method for acquisition of image data of a patient with a magnetic resonance apparatus.
2. Description of the Prior Art
Medical technology imaging systems today assume an important role in the examination of patients. The depictions generated by the imaging systems of the internal organs and structures of the patients are used for diagnosis of pathological causes, for planning of operations, in the implementation of operations, as well as for preparation of therapeutic measures. Examples of such imaging systems are computed tomography systems, ultrasound systems, angiography devices, positron emission tomography systems and magnetic resonance systems.
With a magnetic resonance examination of specific organs or body parts of a patient, surface antennas are increasingly used for acquisition of the magnetic resonance (MR). In the examination these surface antennas are arranged relatively close to the body surface, optimally directly on the organ or body part of the patient to be examined. The surface antennas are frequently executed as a coil and are often designated as “local coils” in the technical literature due to the limited spatial examination region. In contrast to larger antennas arranged further from the patient that normally are used to generate an entire slice image through a patient, the surface antennas have the advantage that they are arranged closer to the regions of interest. The noise component caused by the electrical losses within the body of the patient is thereby reduced, which results in the signal-noise ratio of a surface antenna being in principle better than that of a more remote antenna. A disadvantage is that a single surface antenna is only able to generate an effective image within a specific spatial extent which lies on the order of the diameter of the conductor loops of the surface antenna. The usage possibilities for such individual surface antennas are therefore very limited due to the limited observation range (field of view). The observation range can in fact be expanded by enlarging the diameter of the conductor loop of the surface antenna. However, an increase of the electrical losses in the body of the patient and an associated increase in noise result from the enlargement of the conductor loop. In the use of a single surface antenna, a compromise must always be selected between an optimally good resolution and an optimally large observation range.
One possibility to enlarge the observation range without reducing the resolution to the same degree is to use multiple individual surface antennas arranged adjacent to one another, i.e. to use an entire field of antenna elements (for example an antenna array), that together form one large surface antenna. However, one problem with the use of multiple antenna elements is that the patient can perceive the coverage of body regions over a large area as objectionable, which in extreme cases sometimes leads to a termination of the examination. Moreover, the application of additional sensors (such as electrocardiogram electrodes) is made more difficult given a coverage of the patient over a large area. The high costs that arise due to the purchase of numerous antenna elements represents an additional disadvantage. Moreover, the handling of the individual antenna elements of the multiple elements (i.e. the application and removal of the antenna elements) is time-consuming and therefore cost-intensive. Moreover, the probability of an incorrect placement of the antenna elements on the body of the patient increases with the number of antenna elements, which can lead to an impairment of the image quality. A further disadvantage of the surface antennas placed on or below a patient is in that the position of the surface antennas relative to the body of the patient can no longer be varied during an examination. This means that, given a less suitable placement of the surface antennas, either a poorer image quality must be accepted or a termination of the image acquisition with subsequent, more correct placement is necessary.
Methods and devices to avoid the disadvantages of surface antennas arranged directly on the body of the patient are already known. For example, in United States Patent Application Publication 2002/0138001 a magnetic resonance apparatus is described which itself has a surface antenna that can be lowered from above onto a recumbent patent by a corresponding device. However, the application of a surface coil in the examination space of the magnetic resonance apparatus reduces the space available for the patient. In particular, examinations are known as “head first” examinations in which the patient is inserted head first into the magnetic resonance apparatus can lead to claustrophobic reactions in the patient due to the reduced space. Moreover, the described stationary arrangement at the magnetic resonance apparatus means that the position of the surface coil relative to the electromagnetic fields emitted by the magnetic resonance apparatus cannot be altered. An optimization of the acquisition properties of the surface antenna due to a movement relative to these fields is therefore not possible.
The same is true for the design in United States Patent Application Publication 2005/0174117. There a local coil with flexible properties is described but without information as to how a larger range of the patient can be efficiently examined.
Furthermore, a device in which a local coil is integrated into a bed is described in WO 2006/131863 A1. It is disadvantageous that the local coil therein assumes a stationary spatial position after the insertion of the patient. This means that the position of the local coil can then no longer be optimized, for example in order to correct disadvantageous couplings with other coils in the magnetic resonance apparatus. Moreover, the document refers to coils integrated into a bed, such that essentially only regions on the back side of the patient (such as the spinal column) can be examined.